Linux Icon Functions for Xojo

For next plugin prerelease, we add new LinuxIconMBS module to provide a few new functions to query icons.

The Icon function queries the picture for the icon based on a mime type, while SymbolicIcon queries the symbolic icon. The FileIcon function takes a folderitem and queries a picture for the icon. For some files, you can query a thumbnail with FileThumbnail function. You get back a path to the temporary file with the icon, in our case a png file.